Sinclair swine melanoma represents a unique experimental model for the study of host and cellular mechanisms involved in the spontaneous development, growth and regression of tumors. The objective of this study is to investigate selected host and tumor cell characteristics which can be correlated with the in vivo pathology and natural history of Sinclair swine melanoma. Swine melanoma growth will be evaluated in situ, in vitro, and in immunodeficient hosts. The clinical course of melanoma growth and regression will be monitored by Winn tumor neutralization and lymphocyte microcytotoxicity assays. These basic studies will facilitate more extensive investigations of cellular differentiation, viral participation and host responses involved in this clinically relevant melanoma system.